Electromyography (EMG) refers to evaluating electrical activity produced by skeletal muscles. In particular, EMG measures action potential voltages that neurologically activate muscles. The action potential voltages can be measured from surface electrodes, or intramuscular electrodes that are inserted into a subject's muscle. EMG can be used for therapeutic uses, such as for physical therapy or rehabilitation. EMG has also been used for entertainment, for controlling a video game, for example.